The invention relates to a method of manufacturing a semiconductor device, wherein a semiconductor element is secured to a support plate and provided with a synthetic resin encapsulation, and wherein the support plate is provided with a flange with an undercut region to which the synthetic resin encapsulation is secured. The invention also relates to a semiconductor device obtained by means of said method, and to the manufacture of a support plate which can suitably be used in such a semiconductor device.
A method of the type mentioned in the opening paragraph is known from PCT patent specification WO 95/15578, published on Jun. 8, 1995. In said document it is described how a semiconductor element, in particular a semiconductor diode, is secured to a support plate and provided with a synthetic resin encapsulation. The support plate (see FIG. 6) is provided, by means of turning, with a projecting flange which plays a part in securing the synthetic resin encapsulation. The projection is provided with an undercut region by bending it by means of a die.
A drawback of the known method resides in that it is comparatively laborious and hence expensive.
Therefore, it is an object of the invention to provide a method enabling a semiconductor device to be manufactured in a simple and inexpensive manner, with the encapsulation of said semiconductor device being properly secured to the support plate.
For this purpose, a method of the type mentioned in the opening paragraph is characterized in accordance with the invention in that the support plate is made from a ductile material, a step is pressed in the surface of the support plate by means of a first die, and the flange provided with the undercut region is formed near the wall of the step by means of pressing using a second die. By manufacturing the support plate from a ductile material, it becomes possible to employ exclusively a die-technique to manufacture the entire flange. As a result, a method in accordance with the invention is simple and inexpensive. Providing the method is carried out correctly, a flange manufactured by means of said method and provided with an undercut region bonds satisfactorily to the synthetic resin envelope of the semiconductor element. To achieve this, it is necessary in accordance with the invention that the surface of the support plate is provided with a step by means of a first die. Near said step, a suitable flange provided with an undercut region can subsequently be formed in different ways. All this will be explained in greater detail when the different modifications are discussed hereinbelow.
In a preferred embodiment of a method in accordance with the invention, the support plate is locally recessed by means of the first die, resulting in a recessed portion forming the step in the surface of the support plate, after which a part of the wall of the recessed portion is pressed inwards by means of a second die having a larger width than the first die, resulting in the formation of the flange provided with the undercut region. This modification has important advantages. It only involves two dies and two die steps. A suitable edge provided with the undercut region is formed in a simple manner on either side of, or around, the first and the second die, which has a favorable effect on the adhesion of the encapsulation. In this modification, the semiconductor element can be provided and secured in the recessed portion, which has the additional advantage that the upper surface of the semiconductor element and the support plate can be co-planar. Inter alia the provision of a wire connection between the element and the support plate is simplified thereby.
In a favorable modification, the second die is a hollow die which is formed around the first die. By virtue thereof, the stamping process is simplified, and the second die is automatically accurately aligned with respect to the recessed portion. Preferably, the first die is concave in cross-section, and the cross-section of the second die is (slightly) faceted. By virtue thereof, on the one hand, the side wall of the recessed portion becomes more suitable for the formation of a flange with an undercut region and, on the other hand, such a flange can be formed more easily so as to have a geometry and dimensions which are suitable for a satisfactory adhesion of the synthetic resin encapsulation.
In a further, also favorable embodiment of a method in accordance with the invention, the first die is provided, near an outside, with a recess, and during pressing by means of the first die, a clamping ring is pressed on the surface of the support plate at the outside of the first die, as a result of which the step and a nearby projection are formed next to each other in the surface of the support plate, after which the projection is pressed towards the surface of the support plate by means of the second die which is provided with a facet for this purpose, resulting in the formation of the flange provided with the undercut region. In the space between the projection and the step, a groove is formed, as it were, which contributes to a satisfactory, i.e. strong, adhesion of the synthetic resin encapsulation to the support plate. Also this modification enables a plurality of flanges provided with undercut regions to be simultaneously formed.
Aluminum is a suitable ductile material. This material is light, readily machinable and solderable. Preferably, the flange is formed so as to be a continuous ring-shaped flange which is provided on the inside with the undercut region, and within which the semiconductor element is secured onto the support plate. This results in an optimum bond and simple, for example, circularly symmetrical tools. The semiconductor element can then be provided on the support plate, within the flange provided with the undercut region, after which the semiconductor element is provided with the synthetic resin encapsulation.
The semiconductor device obtained by means of a method in accordance with the invention is not only comparatively inexpensive but also very reliable. The invention also includes a method of manufacturing a support plate which can suitably be used in such a semiconductor device, said support plate being provided with a flange having an undercut region, characterized in that the support plate is made from a ductile material by pressing a step in the surface of the support plate by means of a first die, and the flange provided with the undercut region is formed near the wall of the step by means of pressing using a second die.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter.